What is a CXFEL?

A compact X-ray free electron laser (CXFEL) is a miniature version of the much larger X-ray free electron laser. It not only will be smaller and more cost efficient, it also has the potential of a more precise X-ray beam, with very short pulses. These short pulses make it even more precise than the large XFELs, where photons are fully synchronized in 3D, enabling completely new science and applications.

The ASU CXFEL will see things that cannot be seen with conventional X-rays. The instrument will let scientists see inside molecules, helping them create more effective drugs, find new sources of renewable energy, advance quantum computing and even gain deep insight into archeological and artistic treasures without damaging them.

What is an XFEL?

XFEL devices are linear particle accelerators that start with a riverlike flow of free electrons to produce their ultrafast, brilliant X-rays. Whereas a particle accelerator goes in a circular track of tubes, electrons in a linear accelerator are accelerated to near light speed through a two-mile straight tube. During the course of their flight, the electrons are fed into an undulator — a series of powerful magnets of alternating polarity. As the electrons jiggle up and down under the magnetic field, they emit intense X-rays.

Currently, there are only five X-ray free electron lasers in the world. That is probably because most cost billions of dollars to construct. XFELs also require massive tracts of land and take hundreds of people and $100 million a year to operate.

How is a CXFEL different from an XFEL?

The ASU CXFEL will fit neatly in a traditional lab space at a fraction of its peers’ massive cost.

One of the key innovations that allows the new device to be radically reduced in size is the replacement of the undulator magnets, which force electrons on a wiggling path over a distance of 1 mile. In the compact X-ray light source, or CXLS – the initial phase of the project – the job of jiggling the electrons and inducing them to emit X-ray light is accomplished by colliding the electrons flying at the speed of light head-on with an extremely powerful infrared laser beam with a brilliance that is 80 trillion times higher than a laser pointer.

This is accomplished in a collision zone of 20 micrometers, five times smaller than the diameter of a human hair. The new laser-driven concept reduces the size of the undulator by about 10,000 times and the size of the accelerator by 100 times.

A further breakthrough is required for the transition from CXLS (light source) to CXFEL (electron laser), which involves taking disorganized bunches of electrons and converting them into a precise arrangement or nanopattern.

In addition to size and cost differences, both XFEL and CXFEL devices have different roles to play and lend themselves to different types of experiments. This is analogous to a hammer and a scalpel: XFELs have more powerful beams, while the ASU CXFEL is a more precise tool. 

How does the CXFEL work?

The instrument will accelerate electron bunches to nearly the speed of light through a series of three linear accelerators. Powerful magnets will focus and direct the electrons to collide with the powerful focused infrared laser pulses.

The collision — which generates the power of 100 Hoover Dams, but for only one-millionth of one-millionth of a second — produces short femtosecond X-ray pulses. To provide some perspective, the time difference between a femtosecond and a second is the same as between a second and 32 million years.

This elaborate process will enable scientists to peer into atomic- and molecular-scale structures with unmatched clarity.

The ASU CXFEL will illuminate the processes of life. Proteins are the molecular building blocks of the body and the machinery of cells. They drive all life processes. Until the advent of the XFEL, there was no effective method for observing their movement with the detail and speed needed to understand how they work. Understanding how proteins behave is essential to creating more effective treatments for disease.

When will the ASU CXFEL be in operation?

Phase one of the CXFEL project, building the compact X-ray light source, generated first electrons in February 2021 and is anticipated to be completed in 2023.

Where is the CXFEL located?

The ASU CXFEL is housed in the Beus Compact X-ray Free Electron Laboratory in Biodesign C on the Tempe campus. This is the first time a powerful X-ray accelerator has been built in a public research building at a university.

The basement of the new building has been designed to host two compact X-ray accelerators, the CXLS and CXLS, in a special research space that provides the vibration-free, highly controlled and shielded environment to operate the accelerators. This includes a 30-by-30-foot metal room, acting as a powerful shield of the sensitive high-power lasers from the Klystron power supplies that feed the CXLS/CXFEL.

When the CXFEL is operating, escape of even a trace of X-rays are prevented by 6-foot metal-shielded  walls and doors weighing 860,000 pounds.

The construction team:

  • Minimized vibration from passing light rail trains.
  • Reduced magnetic fields in building materials.
  • Contained the energy from the laser beam.

Making the vibration-free shielded home for the CXLS/CXFEL on a four- to six-foot concrete mat slab required a special overnight pour from more than 100 cement trucks, four-foot thick concrete walls, a Faraday cage structure, demagnetized steel rebar, electronic safety features and a state-of-the-art control room.